Non-Foster Circuits (NFCs) are known per se in the prior art and may be configured as either a Negative Impedance Inverter (NII) or a Negative Impedance Converter (NIC). The former converts the load immittance to its negative inverse (e.g. a capacitor is converted to a negative inductor), and the latter converts the load immittance to its negative value (e.g. a capacitor is converted to a negative capacitor).
J. G. Linvill first reported the possible existence of NIC circuits in “Transistor Negative-Impedance Converters,” Proceedings of the IRE, vol. 41, pp. 725-729, in June 1953.
This invention is an improvement over the Linvill NIC, which is a single ended NIC. Linvill reported 1) a floating NIC that does not provide for NII operation and cannot be tuned by a variable resistor and 2) a grounded NIC that is single ended, and therefore is not appropriate for situations where a floating immittance is needed. The grounded NIC has the disadvantage that bias current must flow either through the load (which is problematic when the load is a capacitor) or around the load (which can cause resonances that lead to oscillation when inductors are used or decrease the performance if resistors are used). In addition, these circuits have been made using discrete transistors with bias networks made of resistive voltage division, which is a different paradigm from Integrated Circuit (IC) design, and results in lower performance when creating negative inductance and capacitance. Others have also made the single-ended Linvill circuit with discrete transistors. See, e.g., S. E. Sussman-Fort and R. M. Rudish, “Non-Foster Impedance Matching of Electrically-Small Antennas, IEEE Transactions on Antennas and Propagation, Vol. 57, August 2009.
R. L. Brennan, T. R. Viswanathan, and J. V. Hanson report NIC IC in CMOS, but it is a single-ended circuit it is considered only for its ability to generate negative resistance. See “The CMOS Negative Impedance Converter,” IEEE Journal of Solid-State Circuits, vol. 32, no. 5, October 1988.
The negative impedance converter (NIC) and inverter (NII) have been known for decades, and there is a long-felt need to use them for antenna impedance matching applications. However, few have succeeded in realizing these circuits due to circuit instability (i.e. the circuits tend to oscillate). It is believed that there have been no previous demonstrations that could feasibly be produced commercially; rather they were demonstrations that had to be tweaked on the bench. This invention satisfies the need of a design that can be mass produced and has been shown to be stable under proper loading conditions.